The human spine serves as the main structural weight bearing support of the human skeleton. The spinal column comprises a plurality of vertebrae separated by intervertebral discs. Moving down the spinal column, five distinct regions exist as follows: cervical, thoracic, lumbar, sacral, and coccygeal. The cervical region comprises seven vertebra; the thoracic region, twelve; the lumbar region, five; the sacral, five; and the coccygeal, four. The cervical, thoracic, and lumbar vertebrae generally remain separate throughout an individual's lifetime whereas the sacral and coccygeal vertebrae fuse to form the sacrum and coccyx, respectively. In general, each vertebra consists of an anterior, cancellous, portion and a posterior arch, comprising two pedicles and two laminae, which support seven processes (four articular, two transverse, and one spinous). The spinal cord runs through a passageway between the anterior and posterior portions of the vertebrae.
When vertebrae and/or intervertebral discs become compromised by trauma, disease, or degeneration, the ability for the spinal column to effectively serve it weight bearing support function is diminished. Furthermore, the spinal cord or nerve roots may subsequently become impinged. As a result, an individual may experience debilitating pain, loss of spinal column stability, and/or reduced range of motion (i.e. flexion, rotation, and extension) of the spinal column. To alleviate these issues, removal and replacement of the compromised vertebrae and intervertebral discs is often required if other non-invasive methods (i.e. drug treatment or physical therapy) prove unavailing.
One common type of vertebral injury is a burst fracture of the thoracic or lumbar portion of the spine, mainly involving the anterior and middle columns, and often occurring in instances of trauma or pathologically from primary or secondary neoplasms. With significant degeneration, spinal surgery becomes necessary for treating the patient. In the past, surgical goals involved spinal stabilization and/or correction of coronal sagittal balance. Accordingly, involved techniques were directed to stabilization of the abnormality and “fusion” techniques. These techniques involve fusing or “freezing” the segment in its position, despite being an abnormal position, in order to prevent progressively worse conditions and to assist in pain relief. This, however, leads to chronic pain as well as progression of abnormal spinal wear and tear, resulting in degeneration of adjacent levels of fused segments. This results in the return of the patient to potentially multiple surgeries finally resulting in Failed Back Surgery Syndrome.
Recent techniques to some degree have taken into consideration the natural balancing of the body. In these, spinal deformity correction surgery is aimed at reestablishing normal physiological coronal and sagittal balance and preserving natural motion of the body. However, even these more recent procedures still fail to take in account many aspects for providing optimal techniques consistent with the body's natural balance and anatomy.